Mechanical longevity estimation model for post-and-core restorations

The aim of this study was to integrate existing knowledge of in vitro strength of post-and-cores and masticatory loading to arrive at longevity estimates for post-and-core restorations when subjected to clinically relevant loads.

A biomechanical model was developed to predict the in vivo longevity. This method was applied to direct post-and-core restorations with amalgam or composite cores. Both experimental laboratory strength values and theoretical clinical strength values were used in the model. The restorations made in the laboratory were assumed to be of a higher quality than clinically made restorations, due to factors such as ease of manipulation, absence of saliva, etc. Both a high and low level of average masticatory loading were considered. The model was used to estimate the probability of mechanical failure before 5 X 10(6) load cycles (5 to 15 years) for all combinations of load range and manufacturing quality.

The calculated failure probability was effectively zero for most combinations except for a clinical quality core subjected to loads in the high range. There the probability of mechanical failure before 5 X 10(6) cycles was estimated to be 2 X 10(-5) for amalgam and 5 X 10(-5) for composite cores. These results agree with the overall observed clinical failure rate of about 1% per year for post-and-core restorations.

The mechanical properties of the post-and-core restorations were adequate for clinically relevant loading conditions.